The effects of SSRI may be mediated via direct serotoninergic effects on the bone cells and SSRIs and the newer antidepressants may affect the cardiovascular system, which may increase the risk of falls. The increased risk of falls may perhaps also be related to muscle weakness stemming from vitamin D deficiency or to effects on the central nervous system affecting postural balance. The risk of falls may explain an early increase in the risk of fractures, whereas any effects on bone density may increase long-term risk of fractures. In depressed patients reduced physical activity may also affect bone via disuse osteoporosis. It is thus not clear if some of the associations previously observed for antidepressants and detrimental skeletal effects may be mediated by the underlying disease (depression), or by factors related to the drugs themselves.